In this study, norepinephrine was tested in 0.1, 1, 10, 25 and 50 mu M doses in 100 mu M NMDA toxicity on cerebellar granular cell culture of rats. NMDA in 100 mu M concentration induced cell death significantly with respect to controls. Death cell population was 1.08 +/- 0.44% in control and 22.15 +/- 2.46% in 100 mu M NMDA (P < 0.0001). None of the norepinephrine concentrations administrated 15 min prior to NMDA was able to reduce death cell scores to control levels. Results were 8.75 +/- 0.83% in 0.1 mu M, 7.0 +/- 1.01% in 1 mu M, 17.25 +/- 1.31% in 10 mu M, 35.5 +/- 1.38% in 25 mu M and 17.9 +/- 1.72% in 50 mu M norepinephrine plus 100 mu M NMDA administrated groups (P < 0.0001 for all with respect to control). Labetalol, as an alpha and beta blocker in 0.5 mu M concentration which was given 15 min prior to norepinephrine was able to block the effects of it. In comparison with 100 mu M NMDA administered group, only low doses of norepinephrine reduced the death cell scores significantly (for 0.1 and 1 mu M norepinephrine plus NMDA groups; P < 0.0001). For 10 and 50 mu M norepinephrine plus NMDA groups, death cell scores were found statistically insignificant from the NMDA-administered group (P > 0.05 for both) while for the 25 mu M norepinephrine plus NMDA group, the death cell score was found to be statistically increased (P < 0.0001). (C) Elsevier, Paris.